Buildings having an enclosed courtyard or atrium can be made more usable, particularly during extreme weather conditions, by having a fabric roof over the atrium. Air-supported fabric roofs have been incorporated into various buildings, for example department stores and schools, and have also been utilized on other structures such as sports stadiums. The publication "Architectural Fabric Structures", Publication No. E36347, from DuPont Company, Fluoropolymers Division, Polymer Products Department, Wilmington, Delaware, shows several such structures, as does the publication "Creating New Environments with Fiberglas, Fabric Structures," Publication No. 5-FS-9789 from Owens-Corning Fiberglas Corporation, Toledo, Ohio (1980).
Fabric roofs are very light in weight, relatively inexpensive, durable, and energy efficient. In addition, fabric roofs pass enough sunlight to permit plants to grow and to provide a pleasant environment even during cold weather.
Air-supported fabric roofs have been of a generally convex shape when viewed from above. Numerous buildings having roofs of various generally convex shapes are depicted in the publication "Architectural Fiberglas Fabric Structures," Publication No. 1-FS-8188-E, from Owens-Corning Fiberglas Corp. of Toledo, Ohio (1982). That same publication points out the general design and construction techniques for such roofs and the problems that must be overcome to successfully use the roofs.
One of the significant problems with air-supported roofs is that, should the air inflation system fail, the roof sags downwardly. Even if sagging of the roof does not present a danger to people, plants, and other objects beneath the roof, still sagging of the roof is likely to damage the roof itself, especially where the roof is supporting a load such as snow. Even the incorporation of a cable restraint, as discussed in the above-mentioned Owens-Corning Fiberglas Corp. Publication No. 1-FS-8188E, does not prevent significant sagging of an air-supported roof, with potentially disastrous results, when the air inflation system fails.
Roofs having a hyperbolic paraboloidal shape offer unique advantages, particularly in covering large areas. Roofs having this shape are substantially self-supporting. Further, over large open spaces of a fixed area, such as courtyards or sports arenas, roofs having a hyperbolic paraboloidal shape may reduce the interior volume by as much as 45% compared with convex roofs, thereby substantially reducing the heating, lighting and other energy costs. This reduced volume is taken from the upper portion of the enclosed space which generally is not utilized, and so the reduced volume does not detract from the usefulness of the structure. Additional advantages of such roofs are described in, for example, the article "Calgary Saddles Up Arena" appearing at pages 50 and 51 of the Dec. 22, 1983 issue of Engineering News Record.